WoW did it ad-nauseum in Pandaria. While I am unhappy with how things look after the questing, I applaud its literary significance.
Alternatively, faction/reputation systems help a lot. Increase your standing with gangs in various planets' underworlds, planetary police forces, political campaigns, by doing jobs for them. Radiant quests work really well here.
Though there needs to be some sort of "incomparable" reward as well. Access to restricted areas is always fun, but the areas have to have some interesting qualities... I shall think much on this.
You're talking about phasing. It's something WoW introduced back in Wrath of The Lich King if I remember right.
Bioware decided against doing this in the development process giving the reason that they didn't want players who were grouping together to get confused or see things differently, ie "I'm standing over by the mail box." "WHAT MAIL BOX!?"
I personally would've liked phasing, but that's the reason that they (Bioware) gave.